It is very important for energy issues to utilize sunlight, which is a permanent and stable energy source. Photosynthesis by plants is an excellent system capable of transforming sunlight energy to chemical energy most efficiently, and absorbs and assimilates carbon dioxide and excess nutrient salts in the environment. In addition, oxygen is emitted. The development of a technology utilizing plants is therefore expected as a solution for energy issues.
Among plants, algae live in both of seawater and freshwater, which abundantly exist; and are therefore huge in amount. In addition, algae have significant photosynthesis ability. Further, some of algae produce a useful compound such as unsaturated fatty acid and anti-tumor compound. Furthermore, since some of diatoms produce a useful inorganic substance, a technology called as biomineralization by diatoms is focused. As described above, algae can be said to be important organisms as useful resources.
When an organism is utilized industrially, a transformation technology for introducing a useful gene is generally used. The transformation technology is also used for knocking out a specific gene or preventing the action thereof in order to elucidate the function of the gene.
The transformation of algae, especially diatoms and green algae, has been conventionally carried out. In such a conventional method, an endogenous promoter is isolated, a gene is conjugated with the promoter, and the promoter is introduced into algae. However, this method is far from efficient, since a lot of effort and time is required for isolating an endogenous promoter. There is also a problem that the transformation efficiency of algae, particularly of marine algae, is originally very low.
On the other hand, in transformation of animals or plants other than algae, a promoter derived from a virus rather than an endogenous promoter is generally used. For example, a CaMV35S promoter isolated from a cauliflower mosaic virus (CaMV) infecting cruciferous plants is used for transforming a wide range of plants without limited to cruciferous plants. For transformation of an animal cell, a CMV promoter isolated from a cytomegalovirus (CMV) and a SV40 promoter isolated from a simian virus 40 (SV40) are widely used.
Unlike the above situation, in transformation of algae, example in which an exogenous virus promoter is used is little known.
For example, Non-patent document 1 discloses an experimental example of transforming a diatom Cycrotela cryptica by using a CaMV35S promoter; however, it is reported that a transformant could not be obtained.
Non-patent document 2 discloses that a GUS (β-glucuronidase) gene was introduced into a diatom Phaeodactylum tricornutum by using a CMV promoter, a CaMV35S promoter or a Rous sarcoma virus (RSV) promoter; as a result, GUS was expressed in any cases.
Non-patent document 3 discloses that when a GUS gene is introduced into dinoflagellate Amphidinium or Symbiodinium by using a CaMV35S promoter, GUS was expressed. However, according to another document (Non-patent document 4), there is no report describing that transformation of dinoflagellates has been succeeded by other group in spite of diligent efforts.